1992 Ford Explorer Top End Clicking Noise Mechanic Told Bad Rocker Assembly

I have a top end clicking noise.A mechanic told me it was a bad rocker assembly.I have one valve cover off (driver side).How do I ckeck to see if the rocker assem.is bad.Or could it be a sticky lifter.I know the old way was to start engine and hold each tappet one at a time to see if noise quieted.Will that method work here on my 92 explorer,4.0 pushrod engine.Not running and cold,the assembly is tite.No play at all.